(1) Field of the Invention
Automatic drafting instruments of the type supporting in parallel a plurality of stylographic pens, each pen having a capillary writing tip. Particularly, a method and apparatus for constantly feeding ink to the several pens so that uniformly wide and full lines are drawn, while eliminating oversupply of ink which results in the formation of a writing fluid drops, at the tip of each pen.
(2) Description of the Prior Art
West German Patent Publication No. 24 29 225 PA0 West German Patent Publication No. 25 22 012
The invention concerns a method for regulating ink flow in drafting pens, especially automatic drafting pens having a cylindrical body with capillary writing tube or tip supported in the forward end of the cylinder. Several such tubular pens may be connected in parallel with a feeding or pumping device for writing fluid. Pumping is controlled by comparing actual ink flow with desired ink flow.
In the case of a known process of this kind, using a single tubular pen (West German Patent Publication No. 22 35 737 or U.S. Pat. No. 3,781,907), the speed of writing with the tubular pen is determined in relation to the drawing base and from this speed of writing an actual value is derived which is supplied to a feeding or pumping device for ink or writing fluid. The feeding device includes a pump which controls the actual value of the amount of writing fluid being fed to the tubular pen. In this manner the tubular pen emits just that portion of writing fluid at any speed during the drawing or writing such that uniformly wide and full lines are drawn. This process involves the difficulty of cutting off without delay the writing fluid supply to the tubular pen as drawing is completed and the tubular pen is lifted off the drawing base. The entire holding device carrying the tubular pen continues to move, of course, after removing the pen from the drawing base, so that a writing speed is thus determinable and an actual value is indicated whereby writing fluid is supplied to the moving tubular pen. Conventionally, this additional supply of ink results in the formation of a writing fluid drop at the writing tip of the tubular pen, so that when the tubular pen is reused a spot forms or a drawn line is enlarged.
In order to avoid these difficulties, it is also already known to measure as actual value the writing fluid pressure occurring in the are of the front end of the tubular pen when drawing with a single tubular pen (German Patent Publication No. 24 29 115, or U.S. Pat. No. 3,950,762) or when drawing with several tubular pens connected in parallel to the feeding device for writing fluid (German Patent Publication No. 25 22 012, or U.S. Pat No. 3,950,762. In this manner, the amount of writing fluid actually being used during the drawing process is determined and, by comparing the actual value with a desired value corresponding to the pressure of the writing fluid in the front area of the end of the tubular pen or tubular pens which is required for a uniform drawing, the supply of the writing fluid to the tubular pen or pens can be controlled in such a manner that the actual value is again and again and practically without delay adapted to the desired value.
Furthermore, the continued movement of the drawing instrument, when the tubular pen is lifted off of the drawing base, has no influence on the supply of the writing fluid because, as soon as writing fluid is no longer being used, the pressure of the writing fluid is automatically adjusted to the desired value, i.e. the value required for optimum drawing purposes. Thus, in the case of this known process, the desired value is that pressure in the writing tip of the tubular pen which is required to permit a uniform flow of writing fluid from the writing tube without formation of spots. When this desired value of writing fluid pressure is maintained, the desired drawing result is obtained, independently of the speed with which the tubular pen is moved relative to the drawing base.
In this way, it is possible, with conventional processes, to vary the drawing speed up to comparatively high values; however, this conventional process requires measuring and evaluation of very small changes in pressure in the magnitude of of fractions or a miniscule number of millimeters of water in a column, so that a very sensitive pressure receiver must be installed in the front area of the tubular pen which must, additionally, interact with a sensitive comparator system for the comparison of desired value and actual value, as well as a sensitive feeding or pumping device for the writing fluid.